Participants
This retrospective study was carried out from January 2016 to December 2019 at the Center of Reproductive Medicine of Mali Hospital, Haikou, China and the Hospital of Shenzhen Immigration Inspection, Shenzhen, China. This study included the first frozen-thawed cleavage-stage embryo transfer (FET) cycle of women who underwent IVF cycles with or without ICSI (Intracytoplasmic Sperm Injection) with an indication of tubal, male, or unexplained infertility. Women with a diagnosis of a congenital or acquired uterine abnormality, such as a uterine malformation, adenomyosis, submucous myoma, uterine fibroids or intrauterine adhesions were excluded from this study. The two post-thawed cleavage-stage embryos for each FET cycle were good-quality embryos that had 7-9 equal size or roughly equal size blastomeres and fragments < 20%, and derived from normally fertilized oocytes. Thawed embryos with damaged blastomeres and the transfer of one or three embryos were excluded.